1. Field of the Invention
The present invention relates to a thin film magnetic head for use in a magnetic disc storage apparatus, that is, a magnetic head whose magnetic circuit and coil are formed of thin films, respectively. More particularly, the present invention relates to a thin film magnetic head having a plurality of magnetic thin film layers.
Thin film magnetic heads are magnetic heads whose magnetic cores and coils are made of thin films, respectively, fabricated and integrated on respective substrates by using semiconductor fabrication technologies.
2. Description of the Prior Art
Referring to FIGS. 1 and 2, an example of the arrangement of a conventional thin film magnetic head will be explained below.
As shown in FIG. 1, a conventional thin film magnetic head has a substrate 1 made of alumina or the like, which has thereon a coil 6. The coil 6 is a spiral coil, and a magnetic core 10 composed of a pair of magnetic core films of an onion-like shape in cross section is placed around a portion of the spiral coil 6 so that the magnetic core 10 sandwiches the spiral magnetic coil 6 at a portion thereof. In a tapered top part 10a of the magnetic core 10, there is provided between the ends of the magnetic core films at one side of the head a one a read-and-write gap G having a narrow gap width g. At a base part 10b of the magnetic core, the other ends of the magnetic core films contact each other to define a magnetic circuit. In a state where the gap G is put close to or in contact with a surface of the disc, the magnetic head can as usual write data on a disc by leading electric current into the coil 6 through a pair of lead wires 9a and 9b, and the magnetic head can read data on a disc by detecting induced electric current in the coil 6.
FIG. 2 is an enlarged cross sectional view taken along line X--X in FIG. 1, showing the portion of the magnetic core provided with the read-and-write gap. As shown in FIG. 2, the magnetic core 6 is composed of a lower magnetic core film 2a and an upper magnetic core film 7a on the substrate 1. The magnetic core 6 is formed as follows. First, the lower magnetic core film 2a, which is about 1 to about 2 .mu.m thick and which is made of a magnetic thin film such as Permalloy, is deposited on the substrate 1. Then there is deposited, on one end of the lower magnetic core film 2a, a thin gap film 3 having a thickness not exceeding 0.5 .mu.m made of alumina or silicon oxide. On the other hand, the other ends of the upper and lower magnetic core films 2a and 7a are joined together. Around the top and base parts 10a and 10b, there are provided the coil conductors 6. In the example shown in FIG. 2, the coil 6 has two-layered turns, i.e., a lower coil part 6a and an upper coil part 6b arranged one above the other, each composed of copper or aluminum deposited by vapor deposition or sputtering and photoetched to have a spiral pattern. The lower and upper coil parts 6a and 6b are supported and covered by lower and upper insulating films 4 and 5, respectively, each made of silicon oxide or polyimide. The upper magnetic core film 7a is formed so as to sandwich the coil 6 between it and the lower magnetic core film 2a, and the lower and upper magnetic core or magnetic pole films 2a and 7a contact the gap film 3 at the top end part 10a of the magnetic core 10. The read-and-write gap G is formed by lapping the outer surface or front face of the top part 10a, and the read-and-write gap G has a narrow gap length g defined by the thickness of the gap film 3 between the lower and upper magnetic core films 2a and 7a. This type of thin film magnetic head as shown in FIGS. 1 and 2 is disclosed in, for example, Japanese Patent Application Laying-open No. 84019/1980.
In the thin head magnetic film having the above-described construction, the lower and upper magnetic core films 2a and 7a are made of high permeability soft magnetic thin films, and endowed with monoaxial anisotropy so that their axis of easy magnetization is fixed to the direction in which the head gap width g is defined.
In order to write on a magnetic medium with a thin film magnetic film at higher density, various efforts have been made to study layered structures of magnetic core films and compositions thereof.
Japanese Patent Application Laying-open No. 90513/1973 discloses a magnetic head including pole pieces each having formed thereon alternately a Permalloy thin film and an alumina thin film, the pole pieces being bonded to each other through a non-magnetic spacer, and coils wound around the pole pieces.
Japanese Patent Application Laying-open No. 38899/1976 discloses a laminate type high permeability magnetic material including a plurality of insulating thin film layers and a plurality of magnetic thin film layers formed on the insulating thin film layers and having a thickness by 0.05 to 2 times as thick as the insulating thin film, the insulating thin film and the magnetic thin film being alternately laminated. The magnetic thin film layer has a thickness of about 0.1 to 10 .mu.m and is composed of Permalloy, Sendust or the like, and the insulating thin film layer is composed of a metal oxide such as SiO.sub.2, TiO.sub.2, Al.sub.2 O.sub.3, GeO.sub.2, Sb.sub.2 O.sub.4, NiO.sub.2, CoO, Fe.sub.2 O.sub.3 or the like or organic polymers.
Japanese Patent Application Publication No. 62162/1992, corresponding to Japanese Patent Application Laying-open No. 192311/1983, discloses a laminate type magnetic material including magnetic layers and non-magnetic layers alternately laminated, in which the non-magnetic layers include two or more types which have different thicknesses. More specifically, the laminate magnetic material includes a substrate, unit film laminates formed on the substrate, each of which is composed of magnetic films each having a thickness of 0.05 to 0.2 .mu.m and composed of Permalloy, Sendust or Fe--Si and first non-magnetic layers composed of SiO.sub.2, Cu, Al, Mo or the like and having a thickness of 10 to 100 .ANG., alternately laminated to a thickness of 1 to 5 .mu.m, and second non-magnetic films each having a thickness of 0.1 to 1 .mu.m, the unit film laminates and the second non-magnetic films being alternately laminated.
Japanese Patent Application Laying-open No. 124108/1989 discloses a thin film magnetic head having a pair of magnetic core films arranged on a non-magnetic substrate in two layers one above another, in which the magnetic core films are composed of a quaternary amorphous alloy consisting essentially of cobalt as a main component and contains further containing hafnium (Hf), tantalum (Ta), and palladium (Pd), especially an alloy composed of Cr, 3.5 to 7 atomic % of Hf, 1 to 4 atomic % of Ta, and 0.2 to 6 atomic % of Pd.
Japanese Patent Application Laying-open No. 112105/1991 discloses a magnetic head including a magnetic circuit a portion of which is made of a multilayer magnetic core film composed of a laminate of an amorphous alloy layer containing Co as a main component and a non-magnetic nitride layer selected from BN, Si.sub.3 N.sub.4, TaN, TiN and W.sub.3 N, alternately laminated one on another.
Recent development of high speed, high density computers has led to operation of thin film magnetic heads at high operation frequencies, and it has been required to develop thin film magnetic heads which can cope with high frequencies above 10 MHz as well as increases in the magnetic flux density. Thin film magnetic heads which can operate at such high frequencies must use magnetic cores having high permeabilities even at high frequencies above 10 MHz.
FIG. 3 is a diagram showing a static magnetic domain structure, in the absence of external magnetic fields, of magnetic core films 2a and 7a used in the aforementioned conventional thin film magnetic head. In FIG. 3, arrows indicate axes of easy magnetization. As will be well understood from FIG. 3, the conventional magnetic core films 2a and 7a each have a circulating magnetic domain structure, with a triangular-shaped magnetic domain 11 being formed at an end 2b, and a hexagonal magnetic domain 12 being formed above the magnetic domain 11. Since the directions of magnetization in the triangular-shaped magnetic domain 11 are parallel to the directions of magnetization from the magnetic recording medium toward the thin film magnetic head, a magnetic domain wall movement occurs at high frequencies. On the other hand, the directions of magnetization in the hexagonal magnetic domain 12 are perpendicular to the directions of magnetization from the magnetic recording medium toward the thin film magnetic head and, hence, there occurs rotation of domain magnetization in an applied high frequency magnetic field. In the magnetic core films 2a and 7a having such constructions, the magnetic domain wall movement in the triangular-shaped magnetic domain 11 does not follow under applied high frequency magnetic fields above several MHz while rotation of domain magnetization in the hexagonal magnetic domain follows up to high enough a frequency. As a result, in the conventional magnetic pole films 2a and 7a, permeability decreases at higher frequencies, which makes it difficult to write and read data in and from a disc. The movement of magnetic domain walls in the triangular-shaped magnetic domain is irreversible at high frequencies and hence it is difficult to perform reproduction of data on a disc in a stabilized manner.